with interconnected ponds. However, comprehensive case studies to quantify factors that affect the accuracy of coastal and interconnected pond maps (Tasks 3b and 3c) were not practical because capabilities to model coastal and shallow flood processes are rapidly evolving. In contrast, methods for riverine flood mapping are more mature and well established. Consequently, the committee simply outlined the accuracy and uncertainty associated with coastal flooding and interconnected ponds.


This report examines FEMA’s mapping methods and recommends ways to improve flood map accuracy and to communicate and manage flood-related information. Chapter 2 describes how FEMA Flood Insurance Rate Maps are created, maintained, and used for insurance, regulatory, and other purposes. Chapter 3 examines the importance of elevation data in flood map accuracy and describes how land and water surfaces are defined relative to geodetic datums. Chapters 4 and 5 analyze factors that affect the accuracy of flood mapping of inland and coastal regions. Chapter 6 assesses the economic benefits of more accurate flood maps. Chapter 7 discusses ways to communicate flood hazard and risk. Methods used to estimate base flood elevations are summarized in Appendix A. Biographical sketches of committee members (Appendix B), a glossary of commonly used terms (Appendix C), and a list of acronyms and abbreviations (Appendix D) appear at the end of the report.

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